A2C3 - Chapter 12 - Homeostasis and the Kidney

Question 1

What is homeostasis?

Answer 1

The maintenance of a state of dynamic equilibrium in the body despite fluctuations in internal and external conditions.

Question 2

Why is homeostasis important?

Answer 2

To ensure optimum temperatures for enzymes and cellular processes in the body.

Question 3

Define negative feedback.

Answer 3

Self-regulatory mechanisms return the internal environment to the optimum when there is a fluctuation.

Question 4

Define positive feedback.

Answer 4

A fluctuation which triggers changes that result in an even greater deviation from the normal level.

Question 5

What is the set point?

Answer 5

A desired value or a range of values determined by a coordinator.

Question 6

Describe receptors and effectors.

Answer 6

Receptors = specialised cells located in sense organs to detect a specific stimulus.

Effectors = muscles or glands which enable a physical response to a stimulus.

Question 7

Describe the role of the coordinator.

Answer 7

Coordinates information from receptors and send instructions to the effectors.

Question 8

State the components of a negative feedback system.

Answer 8

Set point (normal values)
Receptors (detecting change)
Coordinator (coordinates response to change)
Effector (where change comes about from/response to stimulus)

Question 9

What is the mammalian kidney?

Answer 9

One of a pair of organs in the abdomen that has a role in osmoregulation and nitrogenous excretion.

Question 10

What is osmoregulation?

Answer 10

The regulation of water potential of bodily fluids (eg: blood, tissue fluid, lymph) by the kidney.

Question 11

Why is osmoregulation important?

Answer 11

• Prevents cells bursting or shrinking when water enters or leaves via osmosis.
• Cellular reactions occur in aqueous solution therefore, the water levels affect concentrations and rates of reactions in cells.

Question 12

Define excretion.

Answer 12

The process of removing metabolic waste from an organism.

Question 13

Describe how excess amino acids are excreted.

Answer 13

• Amino acids deaminated in the liver (removal of amino group) to form ammonia.
• Ammonia converted to urea (because urea is less toxic)
• Urea is transported into blood plasma and eliminated by kidneys.

Question 14

Identify structures of the excretory system labelled in the diagram.

Answer 14

A = Kidney
B = Renal vein
C = Renal artery
D = Ureter
E = Urethra
F = Bladder

Question 15

What is the function of the renal artery?

Answer 15

Supplies oxygenated blood to the kidneys.

Question 16

What is the function of the renal vein?

Answer 16

Drains deoxygenated blood from the kidneys.

Question 17

What is the function of the ureter?

Answer 17

Takes urine from the Kidneys to the Bladder.

Question 18

What is the function of the urethra?

Answer 18

Releases urine from the bladder, out of the body.

Question 19

Describe the gross structure of a mammalian kidney.

Answer 19

Fibrous capsule = protects kidney
Cortex = Outer region consisting of Bowman’s capsule, convoluted tubules, blood vessels.
Renal Pyramids = cone shaped subdivisions
Renal pelvis = funnel-shaped dilated section of ureter
Medulla = inner region consisting of collecting ducts, loops of henle, blood vessels.

Question 20

What is a nephron?

Answer 20

The functional unit of the mammalian kidney.

Question 21

Where are nephrons found within the kidneys?

Answer 21

Part of the nephron is located in the medulla and part in the cortex.

Question 22

Identify the structures of the nephron labelled in the diagram. (8)
Refer to diagram in memory.

Answer 22

A = Glomerulus
B = Bowman’s Capsule
C = Proximal Convoluted Tubule (PCT)
D = Collecting Duct
E = Afferent Arteriole
F = Efferent Arteriole
G = Loop of Henle
H = Distal Convuluted Tubule

Question 23

Describe the blood vessels associated with a nephron.

Answer 23

Wide afferent arteriole from the renal artery enters the renal capsule and forms the glomerulus, a branched knot of cappilaries which combine to from the narrow efferent arteriole.

The efferent arteriole branches to form a capillary network that surrounds the tubules.

Question 24

Identify the structures of the nephron labelled in the micrograph (idk how ur gna see this lil bro)

Answer 24

1 = Glomerulus
2 = Proximal Convoluted Tubule
3 = Distal Convoluted Tubule

Question 25

Define ultrafiltration.

Answer 25

The removal of small molecules, water and ions from the blood in the glomerulus of the kidney at high pressures.

Question 26

Describe the process of ultrafiltration.

Answer 26

Occurs in the Bowman's capsule. High hydrostatic pressure in the glomerulus forces small molecules (eg urea, water, glucose, ions) out of the capillary fenestrations against the osmotic gradient. Basement membrane acts as a filter. Blood cells and large molecules like proteins remain in the capillary.

Question 27

Why is there a buildup of pressure in the glomerulus?

Answer 27

Afferent arteriole into glomerulus is wider than efferent arteriole going away from the glomerulus.

Question 28

How are cells of the Bowman's capsule adapted for ultrafiltration?

Answer 28

Fenestrations between epithelial cells of capillaries. Fluid can pass between and under folded membrane of podocytes.

Question 29

What happens during selective reabsorption?

Answer 29

Useful molecules from glomerular filtrate are reabsorbed. Eg: glucose, some water and some ions. Involves membrane transport proteins.

Question 30

Where does selective reabsorption occur?

Answer 30

Proximal convoluted tubule.

Question 31

How are cells in the PCT adapted for selective reabsorption? (5)

Answer 31

1. Microvilli = Large SA for co-transport proteins 2. Lots mitochondria = ATP for active transport of glucose into intercellular spaces. 3. Folded basal membrane = Large SA 4. Tight Junctions = stops reabsorbed materials releaking out into filtrate. 5. Peritubular Capillaries = Extend into medulla allowing for reabsorption of materials.

Question 32

By what mechanism are amino acids and filtered glucose selectively reabsorbed into the blood?

Answer 32

Secondary active transport Uses co-transport mechanism involving Na+

Question 33

By what mechanism are mineral ions selectively reabsorbed into the blood?

Answer 33

Active Transport

Question 34

By what mechanism is water selectively reabsorbed into the blood?

Answer 34

Osmosis

Question 35

How are filtered proteins (and some urea) selectively reabsorbed into the blood.

Answer 35

Diffusion

Question 36

Describe the loop of henle.

Answer 36

A loop consisting of a descending limb (dipping into medulla) and ascending limb (rising into cortex) surrounded by blood capillaries.

Question 37

What is the function of the loop of henle?

Answer 37

Creating low water potential in medulla, enabling reabsorption of water.

Question 38

Describe what happens in the loop of henle. 5 steps.

Answer 38

1. Active transport of Na+/Cl- out of ascending limb 2. Water potential of interstitial fluid decreases. 3. Movement of water out of descending limb via osmosis (ascending limb is impermeable to water) 4. Water potential of filtrate decreases going down limb - lowest is in the medullary regionm highest at top of ascending limb. 5. Hair pin counter-current multiplier.

Question 39

What is an endocrine gland?

Answer 39

A gland of the endocrine system that secretes hormones directly into the bloodstream.

Question 40

How is the concentration and volume of urine controlled.

Answer 40

Controlled by the secretion of ADH.

Question 41

Explain the role of the hypothalamus in osmoregulation.

Answer 41

Osmoreceptors in the hypothalamus detect the concentration of the blood plasma. Hypothalamus secretes ADH.

Question 42

Explain the role of the posterior pituitary gland in osmoregulation.

Answer 42

Stores and secretes the ADH produced by the hypothalamus.

Question 43

Describe how ADH affects the reabsorption of water from the kidney tubules. (4)

Answer 43

ADH causes insertion of aquaporins into plasma membranes of the cells of DCT and collecting duct. Increases permeability of DCT and collecting duct. More water reabsorbed More concentrated urine produced.

Question 44

Describe the effects of kidney failure. (4)

Answer 44

There would be a: - Build up of toxic waste eg urea. - Fluid accumulation leading to swelling - High concentrations of renin may lead to hypertension - Low concentrations of EPO leading to anaemia.

Question 45

Outline the potential treatments for kidney failure. (5)

Answer 45

Low protein diet Control of blood calcium and potassium levels Drugs to lower blood pressure Renal dialysis Kidney Transplant

Question 46

Describe renal dialysis.

Answer 46

- Medical procedure artificially filtering the blood - Relies on a partially permeable membrane between the patients blood and dialysis fluid. - Two types: Haemodialysis and Peritoneal Dialysis

Question 47

What is a transplant?

Answer 47

A medical procedure in which an organ or tissue in an individual is replaced.

Question 48

Describe how animal excretory products can differ.

Answer 48

Freshwater animal species secrete ammonia Reptiles, birds and insects secrete uric acid Mammals secrete urea

Question 49

How does the length of the loop of henle differ between mammals?

Answer 49

Length of the loop varies depending on availability of water in the mammals environment. Longer loop in desert animals to allow greater time for reabsorption of water and salts.